This paper is presenting the implementation of the concept of a Visitor Instrument at the Very Large Telescope observatory of ESO at Paranal. The focus on the Nasmyth A of Melipal UT#3 (8m telescope) is dedicated to receive these Visitor Instruments. This concept consists in the installation of an Instrument at the Visitor focus for an observation run for a limited period of time, and then to remove the instrument. The selection of the instrument is done according to its scientific and innovative outcome compared to the other ESO instruments already existing in the observatory. Once granted an observation run of several nights, the visitor Instrument has to show its compliance with the requirements of Paranal Observatory. Then the implementation and integration of the Visitor Instrument are scheduled according to the needs of the Institute who developed the instrument. The instrument is installed at Paranal with the support of ESO staff. The Visitor Instrument can be operated in 2 different modes according to its level of compliance to the ESO specifications. Immediately after the observation run is finished, the instrument is removed from the Visitor Focus.